Woocommerce Discount/Fee from custom attribute

function.php

function ezep_cart_order_total_action(WC_Cart $cart){
  global $woocommerce, $post;
  
  $order = new WC_Order($post->ID);
  $order_items = $woocommerce->cart->get_cart();

  $discount = 0;
  $discount_name = "Descuento por pago en efectivo";
  $payment_method = "";
  $payment_method_desired = "cod";
  $attribute_desired = "pa_cash_price";

  if (isset($_POST['payment_method'])){
      $payment_method = $_POST['payment_method'];
  }

  if ($payment_method == $payment_method_desired){
  
    foreach ($order_items as $order_item_key => $order_item) {
      $_product = new WC_Product( $order_item['data']->post->ID );
      $quantity = $order_item['quantity'];

      $cash_price = 0;
      $cash_price = $_product->get_attribute( $attribute_desired );

      if ($cash_price){
          $price = $_product->price;
          $discount += ( floatval($price) - floatval($cash_price) ) * $quantity ;
      }
    }

    if(!empty($discount) || $discount != 0){
        $discount *= -1; // convert positive to negative fees
        $woocommerce->cart->add_fee(__($discount_name,"woocommerce"), $discount, false, "" ); // add negative fees
    }
  }
}

add_action('woocommerce_cart_calculate_fees', 'ezep_cart_order_total_action');